Fix various documentation, mostly related to file analysis.

- Fix examples/references in the file analysis how-to/usage doc.

- Add Broxygen-generated docs for file analyzer plugins.

- Break FTP::Info type declaration out in to its own file to get
  rid of some circular dependencies (between s/b/p/ftp/main and
  s/b/p/ftp/utils).

src/main.cc

@@ -872,6 +872,7 @@ int main(int argc, char** argv)
 	if ( generate_documentation )
 		{
 		CreateProtoAnalyzerDoc("proto-analyzers.rst");
+		CreateFileAnalyzerDoc("file-analyzers.rst");
 
 		std::list<BroDoc*>::iterator it;